Negative resistance circuits



March 12, 1935. D. PRINZ 1,993,805

NEGATIVE RESISTANCE CIRCUITS Filed June 28, 1955 2 Sheets-Sheet l ,I l l l l lL i 2 3 -I 5. *T *T INV.ENTORV ATTO R N EY March 12, 1935. D. PRINZ NEGATIVE RESISTANCE CIRCUITS Filed June 28, 1933 2 Sheets-Sheet 2 INVENTOR D/ffE/Cfl P/P/A Z ATTORN EY Patented Mar. 12, 1935 Dietrich'P'rinz, Berlin, Germany, a'ssignor to TelefunkeniIGesellschaft fiir Drahtlose Telegraphic Ill-"b. H; Berlin; Germany Application June 28," 1933, Serial No. 678,036

I In Germany. July 22, 193-2 l-Claims. o1; 119471) The E present invention is 1 concerned with the production and use of a drooping discharge characteristic inhi'gh vacuum tubes.

It has been known in'the prior art'thati in high :5- vacuum discharge tubes comprising aheated cathode, or filament, I and additionally "at least two electrodes, a drooping characteristic is ob tainable if at least' one'of the cold electrodes exhibits :adequate 'secondary electron emission. The shape of sucha :characteristicas insured, e. g., by theinter-relationship between grid'voltage and gridcurrent in' the presence or positive plate" potential ina-standard triode tube isirepr'esented in Fig. 1. The current initiallyrises to positive values seeing .thatiin :the presence :of small grid voltages no' secondary electrons are as yet generated, and it. reaches negative ranges only where largerxpositive grid'potentials are attained.

For a better understandingo'f the invention ref erence is made totheiaccompanying drawings, in

which: s

Figspl, 2.14, 7 andv9show characteristic curves of certain tube arrangements described,

Fig. 3.is a circuitdiagram'of avacuumtube arrangement utilizingxanegative resistance characteristic such asthat .ofrFig. 2,: I

Fig. 5 isa circuit diagram ofanoscillator-arrangement made'according :to' the invention,

Fig. 6 is-an'amplifier'circuit diagram, and

Fig. 8 is an amplifier device connected and arranged according to the invention.

The object of 1 the invention resides in the production of a'characteristic. inwhich the current fromthe very outset assumes negative values, as shown in Fig. 2, instead of assuming initially positive values as-shown'in' Figl. According to the present invention,.with. the said end in view, re-j course is had' to a tube equipped with twogrids, say, a screen'grid type of. tube. Thekey diagram used therefor is shown in Fig. 3. The-inner, grid (control grid) is given such a high negative biasing voltage that atcurrent Will' be ableto'fiow to the outermost-grid (screen grid) :and towardsthe plate only in the presenceof such high screen grid potentials that the coefficient ofsecondary electron emission of the screen-grid becomes essentially greater than unity (1) ;.in other words,

that thenumber-"of electronsissuing from the screen grid is greater than the numberof electrons impinging thereon. The result is that the :screen grid current will havea negative value from its very incipiency so that the graph giving the relationship between screen grid voltage and screen grid current will havea shapetasiillu'strated in Fig. 2. Supposing that the coefficient of secondary emission is essentially constant, then the resultant negative screen grid current will be proportional to the originally primary screen grid current, and will have the formof a normal space charge curve 1'= 'K.V oomprising a negative factor of pro-' portionality K- 1 Now, according to'the present invention, this fact is used for the object of producing characteristics of extremely high positive or negative slope. What is used to that end is a standard triode tube whose mechanical dimensions and whose grid biasing voltage are so chosen that its character istic is just thereflected image of the drooping characteristic shown in Fig. 2 in'fact, a charac-' teristic of this kind is represented on therighthand side in Fig. 4. on the other hand, by simple reversal of polarity of an arrangementshownin Fig; 3, Wh8,l; is obtained from the characteristic Fig. 2 is a characteristic which is shown on the left-hand side in Fig. 4. In other words the device of'Fig. 3 gives the characteristic curve of Fig. 2 when the positive direction for current is taken as into the screen grid from the cathode and positive direction of voltage is cathode-negative, screen grid positive. If now" the polarityof therbasic plus directions for voltageand currentzare reversed we get the characteristic'shown at the left sideofFig.4.

.By connecting series the said two arrangements what is then obtained is a characteristic which is due 'to that the voltage values corresponding to avdefinitevalue. of thecurrent, and shown-by the curves in the left hand and the right hand side in Fig. 4, are added to one another.

However, owing to the symmetry of these curves what. results is a straight line which coincides with the current axis, and which, in other words, possesses an infinitely great. slope, theoretically speaking. -But, by'p'roviding slight departures in the shapev of the two characteristicsconditions in practice can be made so that this slope will assume veryhigh. and finite positive or negative values.

Fig. .5 shows the use .of such an arrangement forthe purpose of'wave generation. Referring to the same, ldenotes the screen gridtubewhich furnishes a characteristic as ill-Fig; 2'0r the curve on the left hand side Fig. 4'; 2 denotes the plain, or single grid, tubezwhose characteristic isshown on the right hand .side', Fig.4. 3 and 4 are the inductance. and capacity comprisedin an oscil-v lation. circuit which determines the frequency of the oscillations generated. ''Now, it is well-known that the production of oscillations by'the aid of Now, basically speaking, it is feasible to insure very great slope,values by that any desired drooping characteristic of the dynatron type is arranged in series with a resistance the size of which corresponds to the maximum slope of this characteristic. However, owing to the curvature of the characteristic, the new characteristic which results because of the addition of the resistance will have an infinitely great slope only in the immediate neighborhood of the point Where the original characteristic had its maximum slope. thus generated will be able to assume only very small amplitudes. However, in an arrangement as here disclosed, by the combination of a rising and a drooping characteristic of practically identical forms, an extremely great slope is attained inside a wide range of potential as has been explained above in more detail. The result is that with such an arrangement oscillationsof considerably larger amplitude are generable. In the oscillator arrangement of Fig. 5, the rising characteristic of the triode 2 is balanced as it were by the drooping characteristic of the screen circuit of tube 1 so that a resultant very steep characteristic, such as that shown by the part of the current axis which is made heavy,

in Fig. 4, is obtained. Under these conditions a very small change in grid voltage of tube 2 will producea large change in its plate current,

Another application resides in the amplification of alternating potentials in a circuit scheme known as resistance-coupled amplifiers. The principle underlying is indicated in Fig. 6; Ra denotes the external resistance, Ea the plate battery. The operation of such a circuit scheme is representable as well known in the following manner:

For two different gridvoltages, say, I() and 11 V. one plots the graphs giving the interrelationship between the plate current Ia and the plate voltage Va (Fig. 7). In this diagram is plotted, furthermore, the characteristic of the system which consists of the plate battery Ea and the external resistance Ra.

This characteristic is a straight line intersecting the Vaaxis at the point Where Va Ea, and which presents an inclination being the reverse of the inclination of the characteristic of resistance Ra itself; in other words, which exhibits a tendency towards increasing currents with decreasing potential. The points of intersection between this straight line and the tube characteristics then result in currents In and I82 andvoltages Val and Vera which flow through or are active across the tube in the presence of grid potentials .l0 and -11 V. The difierence VazVa1 in other words, results inthe, plate potential difference per 1 V grid potential dif-v The result is that waves The operation of the arrangements shown in Fig. 8 fiows from Fig. 9. Instead of a straight line, Fig. 7, there is obtained here a curve which is obtained from the curve Fig. 2 by tilting the same over, and the applied plate potential Ea may become here of zero value, if dimensions arechosen appropriately. As can be readily seen the whole or. resultant characteristic of the amplifier arrangement of Fig. 8 is covered by a change of .1 V in'the grid potential so that the differences VazVa1 and Ia2Ia1 are substantially'greater than the use of an ordinary resistance. The'resultant characteristic is shown by the middle curve of Fig. 9 from which it is tions may beutilized by connecting to the triode,

plate-circuit. In other words, thetube arrange ment shown'is Fig. 8 aifords'a far higher gain. What should also be mentioned is thatthe arrangement as here disclosed offers this advantage over other arrangements known from the,

prior art in which the plate circuit of the amplifier "contains another discharge tube acting as an external resistance, that the said second tubeis not connected the reverse of the first, but that its filament is united with the filament of the first tube so that harmful effects due to ground: capacitance of the sources of the filament are unable to arise.

- What is claimedis:

1. An amplifier arrangement comprising the combination of a triode having a cathode, a control'grid and plate, a second tube having a cathode, a first grid, a plate and a screen grid 1 cated between said first grid and plate, a circuit icoupling said triode plate to said screen grid, and means connected to impress a high negative'biasing voltage on said first grid.

2. The combination defined in the preceding claim in which a conductive connection is provided to connect the cathodes of thetubes.

3. An amplifier arrangement comprising the combination of a triode having a cathode, a control grid and a plate, a second tube having a first grid, a screen grid anda plate, means for applying a high positive potential to the last named plate, means for applying a high negative biasing voltage to saidfirst grid whereby said screen grid emits secondary electrons and a leadconductively connecting said screen grid and said triode plate.

4. A circuit arrangement comprising a vacuum tube having a cathode, a control grid, a plate,

and a screen grid positioned between the control grid and plate, means for applying a high positive potential to said plate, means for applying a lesser positive potential .to said screen grid than that applied to said plate, and means for applying such a high negative biasing voltage to said control grid that there is no flow of electrons from the cathode into the screen grid and also the flow of secondary electrons from the screen grid increases as its voltage is increased.

DIETRICH PRINZ. 

